**Ester linkages occur in lipids.**

**Explanation:**

Lipids are a diverse group of biomolecules that are insoluble in water but soluble in organic solvents. They play important roles in storing energy, providing insulation, cushioning organs, and serving as structural components of cell membranes. Ester linkages are one of the key types of chemical bonds found in lipids.

Ester linkages are formed by the condensation reaction between a carboxylic acid and an alcohol. The reaction involves the removal of a water molecule, resulting in the formation of an ester bond. This process is also known as esterification.

Lipids, such as triglycerides, phospholipids, and waxes, contain ester linkages. Let's take a look at some examples:

1. **Triglycerides:** Triglycerides, also known as fats, consist of glycerol (an alcohol) and three fatty acids (carboxylic acids). The ester linkages form between the hydroxyl groups of glycerol and the carboxyl groups of the fatty acids. Triglycerides are the primary form of energy storage in animals and plants.

2. **Phospholipids:** Phospholipids are a major component of cell membranes. They consist of glycerol, two fatty acids, a phosphate group, and a polar head group. The ester linkages form between the hydroxyl groups of glycerol and the carboxyl groups of the fatty acids.

3. **Waxes:** Waxes are found in various organisms and serve as protective coatings. They consist of long-chain fatty acids and long-chain alcohols. The ester linkages form between the carboxyl groups of fatty acids and the hydroxyl groups of alcohols.

Ester linkages are not found in proteins (which are composed of amino acids linked by peptide bonds), nucleic acids (which are composed of nucleotides linked by phosphodiester bonds), or carbohydrates (which are composed of monosaccharides linked by glycosidic bonds).

In summary, ester linkages are a characteristic feature of lipids, playing essential roles in their structure and function.